Here two plates moves from each other. Molten rock, or magma, immediately rises to fill any possible gap and forms new crust.
When this happens underwater, it is described as . Huge underwater ranges are formed from magma coming up from the mantle. Over time these submarine volcanoes may become large enough to reach the surface. eg. Iceland in the North Atlantic Ocean. Where plates move apart on land, are formed. An example of this is the Rift Valley.